Crude oil produced from geological formations can contain various amounts of water. Water and crude oil are naturally non-miscible. However, when naturally occurring interfacially active compounds are present, these compounds can aggregate at the oil and water interface and cause water to form droplets within the bulk oil phase. During crude oil lifting through production tubings, the oil and water encounters increased mixing energy from rapid flow through chokes and bends. This additional mixing energy can emulsify the oil and water. This oil external, water internal two-phase system is commonly referred to as a crude oil emulsion. This emulsion can be quite stable.
The presence of water in crude oil can interfere with refining operations by inducing corrosion, increasing heat capacity and reducing the handling capacity of pipelines and refining equipment. Therefore, crude oil that is to be shipped out of the oilfield should be practically free of water and usually has a maximum water content limit of about three percent, depending on the type of crude and oil company specifications.
The crude oil associated emulsified water can also contain varying amounts of salts. These salts are detrimental to crude oil refining processes due to potential corrosion and foulant deposition in the refinery. In crude oil refining, desalting techniques comprise the deliberate mixing of the incoming crude oil with fresh “wash water” to extract the water soluble salts and hydrophilic solids therefrom. The mixing action of heat exchangers and mix valves can produce an emulsion. However, the crude oil routed to refinery distillation equipment is usually required to have less than 0.5 percent water.
Primary dehydration of the crude oil occurs in oil field water oil separation systems such as “free water knock out” and “phase separators”. Refineries employ electrostatic desalters to separate crude oil from the wash water. Quite often these systems are not adequate for efficient separation due to factors such as overcapacity, unexpected production changes and system underdesigns. In these cases, emulsion breaking chemicals are added to the production or refining processes to assist and promote rapid separation of water from oil.
Commonly used emulsion breaking chemicals include alkylphenol formaldehyde resin alkoxylates (AFRA), polyalkylene glycol (PAG), organic sulfonates, and the like. These compounds, however, may not provide satisfactory performance in all instances. Accordingly, there is an ongoing need for new, economical and effective chemicals and processes for resolving emulsions into their component parts of oil and water or brine.